1. Field of the Invention
The present invention relates generally to a sheet processing apparatus capable of stapling a sheet bundle at a plurality of points and to an image forming apparatus that uses this sheet processing apparatus. The present invention relate, more particularly, to a sheet processing apparatus and an image forming apparatus that reduce the time required for the stapling process at the plurality of points and improve the productivity without scaling up the apparatus, causing any complicated configuration of the apparatus and increasing the costs.
2. Description of the Related Art
A conventional type of sheet processing apparatus used for an image forming apparatus is exemplified by an apparatus capable of stapling a sheet bundle of which sheets are stacked and aligned on an intermediate processing tray in a way that moves a stapler sequentially to positions corresponding to a plurality of stapling points thereof.
For example, in the case of executing a stapling process of stapling the single sheet bundle at one point of an angular portion of this sheet bundle on the intermediate processing tray, the stapler stands by in a state of being inclined at a predetermined angle in the position corresponding to the predetermined sheet bundle angular portion. Then, the sheet bundle, of which the sheets are aligned on the intermediate processing tray, undergoes the stapling process at one point of the angular portion thereof by the stapler standing by in the angular portion stapling position. The sheet bundle subjected to the stapling process at one point of the angular portion thereof is thus made.
Many of the sheet processing apparatuses have, in the case of carrying out the stapling process of stapling the sheet bundle as described above, a buffering mechanism that is provided an upstream portion of the processing tray and is capable of temporarily storing (buffering) the sheets so as to prevent a new sheet from entering (approaching) the processing tray. For actualizing faster processing, however, there is no alternative but to conduct such intermittent operation control as to temporarily stop an image forming process on the sheet on the side of an image forming apparatus main body and to resume the image forming process after completing the stapling process during a period for which the sheet bundle stapling process is executed within the sheet processing apparatus. Accordingly, in the case of performing the sheet bundle stapling process as described above, such a problem arises that the productivity decreases to a degree corresponding to the time required for this stapling process.
It is considered as a contrivance for reducing the time required for the stapling process to speed up the stapling process in the stapling position of the stapler. Actualization of this speed-up involves power-up of a drive motor related to the stapling by the stapler. In this case, there are considered problems such as cost-up derived from the power-up of the motor, scale-up of the apparatus and a rise in operating sound level.
Moreover, in the case of executing the stapling process at two points of the single sheet bundle on the intermediate processing tray, the stapler standing by in a first stapling position carries out the stapling process at a first point of the sheet bundle aligned on the intermediate processing tray. Subsequently, the stapler is moved to a second stapling position substantially in parallel with an edge portion of the sheet bundler, wherein the same stapling process as the stapling process at the first point is executed in the second stapling position. The sheet bundle undergoing the two-point stapling process is thus made.
The two-point stapling process of the sheet bundle described above is executed by such control operation that the stapler, after stapling the sheet bundle at the first point, moves by a desired pitch along the edge portion of the sheet bundle and repeats the same stapling process at the second point as at the first point. Therefore, such intermittent operation control is conducted that the image forming process on the sheet on the side of the image forming apparatus main body is temporarily stopped and the image forming process is resumed after completing the stapling process during the execution of the two-point stapling process of the sheet bundle within the sheet processing apparatus. Accordingly, in the case of two- or more-point stapling process, the problem arises, wherein the productivity decreases to an extent corresponding to the time required for this stapling process.
It is considered as a contrivance for reducing the time required for this stapling process to (a) speed up a pitch-to-pitch movement of the stapler or the stapling process in the stapling position, or (b) to decrease a moving quantity of the stapler. These methods, however, present the following problems that are to be considered.
To begin with, the actualization of the method (a) involves the power-up of the drive motor related to moving the stapler or the power-up of the drive motor related to the stapling by the stapler. In this case, however, such problems are considered as to cause the cost-up derived from the power-up of the motor, the scale-up of the apparatus and the rise in the operating sound level.
Further, it is considered for actualizing the method (b) that, e.g., two pieces of staplers are provided in the respective stapling positions in order to execute the stapling process at two points without moving the stapler. In this case, however, the number of the staplers must be increased corresponding to the number of the stapling points, and this brings about, it is considered, a problem of resulting in the cost-up.
For others, Japanese Patent Application Laid-Open No. 2001-220055 discloses a technology of reducing the time required for the stapling process. According to the technology disclosed in Japanese Patent Application Laid-Open No. 2001-220055, on the occasion of moving the stapler, the sheet bundle is moved in a direction opposite to a moving direction of the stapler, thereby reducing the time required for the stapling process in a way that decreases a moving distance of the stapler itself. This configuration is effective in reducing the time required for the two-point stapling process but is not effective in reducing the time required for the one-point stapling process. Further, this configuration needs a mechanism for moving an aligning member in synchronization with the pitch-to-pitch movement of the stapler, and hence such problems are considered that the construction gets complicated and the costs rise.